Diagnostic Aids

WARNING: This page is about a different car, the 2003 GMC Savana and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:

Variable thickness brake rotors.
Drive shaft not balanced.
Worn or damaged accessory drive belt.

There may be more or less cylinders actually misfiring than indicated by the scan tool. Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or misfiring.